1. Field of the Invention
The present invention relates to a transcoder for decoding an input image into a decoded image and encoding the decoded image into an output image.
2. Description of the Background Art
Image compression techniques are widely used for reducing transmission load and storing load of image data. There are MPEG 2 and the like as conventional coding systems, and H.264 and the like as new coding systems. A transcoder executes system conversion between different coding systems for reducing transmission load and storing load of image data.
As a first stage, a transcoder inputs a compressed image according to a first coding system to generate an extension image according to the first coding system. As a second stage, the transcoder compresses the extension image according to a second coding system to output a compressed image according to the second coding system.
A coding apparatus disclosed in Japan Patent Application Laid Open Gazette No. H10-313463 compresses an input image to output a compressed image. The coding apparatus controls a code amount such that an output code amount is equal to or less than a constant target code amount. The coding apparatus disclosed in Japan Patent Application Laid Open Gazette No. H10-313463 also controls a code amount in a same manner as described above even when the apparatus is included in a transcoder as a component thereof.
The coding apparatus disclosed in Japan Patent Application Laid Open Gazette No. H10-313463 controls a code amount such that an output code amount is equal to or less than a constant target code amount. There is a possibility that the coding apparatus drastically deteriorates image quality after compression compared with that before compression when an input image is a fine image or an image of much movement. There is also a possibility as described above when the coding apparatus disclosed in Japan Patent Application Laid Open Gazette No. H10-313463 is included in a transcoder as a component thereof.